"Electrostatic Chuck Patents--United States and Europe", 90100363A-GEN, Nov. 17, 1990 by Sematech, Inc. is a compilation of patent publications in this area. Items of particular interest are briefly discussed below:
U.S. Pat. No. 4,184,188 to Briglia appearing at page 58 of said compilation teaches the holding of a workpiece on a chuck by electrostatic forces without the need for electrical contact with the workpiece.
U.S. Pat. No. 4,384,918 to Abe appearing at page 62 of said compilation shows how the design of Briglia can be simplified by using twin semi-circular electrostatic plates for providing the electrostatic force.
European patent application O 138 254 appearing at page 229 of said compilation (particularly the passage on page 232 lines 20 and 21) indicates that it can take 24 hours for the electrostatic forces to dissipate sufficiently for a workpiece to be removed from an electrostatic chuck. The present invention overcomes this problem by virtue of permitting immediate removal of the workpiece 2 from the electrostatic chuck 4.
United Kingdom patent application 2 147 459 A, appearing at page 346 of said compilation, shows an air jet for releasing a workpiece from an electrostatic chuck.
PCT International Publication Number WO 88/09054, appearing at page 362 of said compilation, discloses (see claims 5 and 6) the use of sapphire and boron nitride substrates for an electrostatic chuck. This reference does not suggest that the reason for using sapphire and boron nitride is for their anti-stick properties (as in the present invention). We can assume it is not for their anti-stick properties, because this reference is limited to a.c. field excitation: the use of a.c. provides the anti-stick function. The only mention in the reference of the purpose for using such a substrate is the passage at p.4 lines 22-30, wherein it is stated that in a radio frequency etch apparatus, high electric fields are required to obtain strong holding forces; and good radio frequency power transfer through the chuck is also a requirement. In such a case, the substrate may be a ceramic, e.g., sapphire.
Note also the following additional references: U.S. Pat. Nos. Re. 32,024; 3,710,251, 4,473,455; 4,547,247; 4,623,839; 4,665,360; 4,666,291; and 4,953,287. U.S. Pat. No. 4,473,455 is illustrative of devices that use mechanical clamps to physically clamp the workpiece onto the chuck. This is undesirable because it wastes space on the workpiece, wastes time due to the requirement for periodic cleaning of the clamps, and can cause damage to the workpiece.
Also see Japanese patent publications 1-281835; 3-3249; 3-3250; and 59-4433; and European patent publication 0 107 323.